Pathways of tundra encroachment by trees and tall shrubs in the western Brooks Range of Alaska
(2020) In Ecography 43(5). p.769-778- Abstract
Climate change is expected to increase woody vegetation abundance in the Arctic, yet the magnitude, spatial pattern and pathways of change remain uncertain. We compared historical orthophotos photos (1952 and 1979) with high-resolution satellite imagery (2015) to examine six decades of change in abundance of white spruce Picea glauca and tall shrubs (Salix spp., Alnus spp.) near the Agashashok River in northwest Alaska. We established ~3000 random points within our ~5500 ha study area for classification into nine cover types. To examine physiographic controls on tree abundance, we fit multinomial log-linear models with predictors derived from a digital elevation model and with arctic tundra, alpine tundra and ‘tree’ as levels of a... (More)
Climate change is expected to increase woody vegetation abundance in the Arctic, yet the magnitude, spatial pattern and pathways of change remain uncertain. We compared historical orthophotos photos (1952 and 1979) with high-resolution satellite imagery (2015) to examine six decades of change in abundance of white spruce Picea glauca and tall shrubs (Salix spp., Alnus spp.) near the Agashashok River in northwest Alaska. We established ~3000 random points within our ~5500 ha study area for classification into nine cover types. To examine physiographic controls on tree abundance, we fit multinomial log-linear models with predictors derived from a digital elevation model and with arctic tundra, alpine tundra and ‘tree’ as levels of a categorical response variable. Between 1952 and 2015, points classified as arctic and alpine tundra decreased by 31% and 15%, respectively. Meanwhile, tall shrubs increased by 86%, trees mixed with tall shrubs increased by 385% and forest increased by 84%. Tundra with tall shrubs rarely transitioned to forest. The best multinomial model explained 71% of variation in cover and included elevation, slope and an interaction between slope and ‘northness’. Treeline was defined as the elevation where the probability of tree presence equaled that of tundra. Mean treeline elevation in 2015 was 202 m, corresponding with a June–August mean air temperature > 11°C, which is > 4°C warmer than the 6–7°C isotherm associated with global treeline elevations. Our results show dramatic increases in the abundance of trees and tall shrubs, question the universality of air temperature as a predictor of treeline elevation and suggest two mutually exclusive pathways of vegetation change, because tundra that gained tall shrubs rarely transitioned to forest. Conversion of tundra to tall shrubs and forest has important and potentially contrasting implications for carbon cycling, surface energy exchange and wildlife habitat in the Arctic.
(Less)
- author
- Terskaia, Anna LU ; Dial, Roman J. and Sullivan, Patrick F.
- publishing date
- 2020-05
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- alpine tundra, arctic tundra, caribou, Dall's sheep, treeline, white spruce
- in
- Ecography
- volume
- 43
- issue
- 5
- pages
- 10 pages
- publisher
- Wiley-Blackwell
- external identifiers
-
- scopus:85079032398
- ISSN
- 0906-7590
- DOI
- 10.1111/ecog.05015
- language
- English
- LU publication?
- no
- additional info
- Publisher Copyright: © 2020 The Authors. Ecography published by John Wiley & Sons Ltd on behalf of Nordic Society Oikos.
- id
- 9f792ffe-991c-4ebf-a83e-b333bffba46b
- date added to LUP
- 2024-07-01 10:25:29
- date last changed
- 2025-04-04 15:24:47
@article{9f792ffe-991c-4ebf-a83e-b333bffba46b,
abstract = {{<p>Climate change is expected to increase woody vegetation abundance in the Arctic, yet the magnitude, spatial pattern and pathways of change remain uncertain. We compared historical orthophotos photos (1952 and 1979) with high-resolution satellite imagery (2015) to examine six decades of change in abundance of white spruce Picea glauca and tall shrubs (Salix spp., Alnus spp.) near the Agashashok River in northwest Alaska. We established ~3000 random points within our ~5500 ha study area for classification into nine cover types. To examine physiographic controls on tree abundance, we fit multinomial log-linear models with predictors derived from a digital elevation model and with arctic tundra, alpine tundra and ‘tree’ as levels of a categorical response variable. Between 1952 and 2015, points classified as arctic and alpine tundra decreased by 31% and 15%, respectively. Meanwhile, tall shrubs increased by 86%, trees mixed with tall shrubs increased by 385% and forest increased by 84%. Tundra with tall shrubs rarely transitioned to forest. The best multinomial model explained 71% of variation in cover and included elevation, slope and an interaction between slope and ‘northness’. Treeline was defined as the elevation where the probability of tree presence equaled that of tundra. Mean treeline elevation in 2015 was 202 m, corresponding with a June–August mean air temperature > 11°C, which is > 4°C warmer than the 6–7°C isotherm associated with global treeline elevations. Our results show dramatic increases in the abundance of trees and tall shrubs, question the universality of air temperature as a predictor of treeline elevation and suggest two mutually exclusive pathways of vegetation change, because tundra that gained tall shrubs rarely transitioned to forest. Conversion of tundra to tall shrubs and forest has important and potentially contrasting implications for carbon cycling, surface energy exchange and wildlife habitat in the Arctic.</p>}},
author = {{Terskaia, Anna and Dial, Roman J. and Sullivan, Patrick F.}},
issn = {{0906-7590}},
keywords = {{alpine tundra; arctic tundra; caribou; Dall's sheep; treeline; white spruce}},
language = {{eng}},
number = {{5}},
pages = {{769--778}},
publisher = {{Wiley-Blackwell}},
series = {{Ecography}},
title = {{Pathways of tundra encroachment by trees and tall shrubs in the western Brooks Range of Alaska}},
url = {{http://dx.doi.org/10.1111/ecog.05015}},
doi = {{10.1111/ecog.05015}},
volume = {{43}},
year = {{2020}},
}